(1) Field of the Invention
The present invention relates to the general subject of electronic power supply converters for energy wherein one example is a boost converter system having a power factor correction (PFC) that is running in discontinuous mode using an equation to calculate the point of time the zero-current state of the storage inductor occurs without the requirement of a secondary winding or special voltage comparators to detect zero current to achieve maximum power transfer and to avoid a continuous mode operation.
(2) Description of the Prior Art
The design of a boost converter system with a power factor converter (PFC) requires small storage inductors together with high transferred power. These two parameters are counteracting against each other. The transferred power reaches its maximum if the storage inductor is recharged right after the inductor reaches the zero current state.
Prior art power supplies are using either secondary windings, special voltage comparators or analog current sensing circuits to detect the zero-current state of the storage inductor.
U.S. Pat. No. 5,757,166 to Sodhi teaches a power correction factor boost converter. A secondary winding is used for zero current detection of the storage inductor.
U.S. Pat. No. 5,861,734 to Fasullo et al describes a control system for a boost converter using 2 interleaved boost circuits. A current sensing circuit is provided that senses the current in each of the boost converters. 2 boost converter switches have to be controlled.
U.S. Pat. No. 6,178,104 B1 to Nak-Choon-Choi describes a power factor correction circuit using reverse saw tooth waves. The switch is coupled to a resistor and a capacity that by forming a current detector, detect the current flowing through the storage inductor of the boost converter. The PFC circuit is using reverse saw tooth waves and is controlling the slope of the current.
Fine adjustment of the energy transfer overcoming the limitations of discrete time in digital systems is a known problem. U.S. Pat. No. 6,043,633 to Lev et al. discloses a method and an apparatus for controlling a boost converter that offers power factor correction by compensating for the parasitic capacitance and parasitic oscillations. A zero current detector facilitates the compensation. A dithering method to enhance the time resolution of clocked digital circuits is presented.
A principal object of the present invention is to provide a highly effective electronic power supply converter such as a boost converter having maximum power, related to the size the of the storage inductor, transferred without the requirement of a secondary winding or voltage comparators.
A further object of the present invention is to provide a highly effective boost converter with a power factor corrector (PFC) having maximum power, related to the size the of the storage inductor, transferred without the requirement of a secondary winding or voltage comparators.
A further object of the present invention is to recharge the storage inductor right after the point of time when zero current state occurs at the storage inductor. This is key to a maximal transfer of energy.
A still further object of the present invention is to achieve a fine adjustment of the energy transfer to minimise distortion and harmonics overcoming the limitations of discrete time steps in clocked digital systems.
Another still further object of the present invention is to achieve an optimal accuracy of the measurement of the voltages at the source and the load side to achieve best accuracy to define the point of time of the zero current state of the storage inductor and furthermore to achieve best accuracy required as input for the fine-tuning of the energy transferred.
Another still further object of the present invention is to achieve less manufacturing costs and to reduce the number of components required by avoiding secondary windings or voltage comparators for the zero current detection.
In accordance with the objects of this invention a system used for converting electronic power supply energy has been achieved. This system can be used as a boost converter or a DC to DC converter. Maximal power is transferred by recharging the storage inductor right after the point of time when zero current occurs at the storage inductor, As an example of the usage of the invention a boost converter with PFC (power-factor-corrector) having maximal power transferred related to the size of the storage inductor by recharging the storage inductor right after the point of time when zero current state occurs at the storage inductor is achieved. FIG. 1 illustrates the main components of the system. The boost converter is including a storage inductor coupled to an input voltage, a shunt switch controlling a current flowing through said storage inductor and a rectifying diode for rectifying the output voltage. Furthermore the system comprises of an analogue/digital converter which is converting analogue values measured and reference voltages into digital values required by a digital control unit to control frequency and pulse width of the shunt switch using means to calculate the point of time when zero current state occurs instead of detecting this point of time using secondary windings or other analog circuits. Said digital control unit initiates the recharging of the storage inductor right after the point of time of the zero current state is reached.
In accordance with an object of the invention a method of calculating the point of time of the zero current state of the storage inductor is achieved. Said point of time is calculated using an equation based on the ON time of said shunt switch and the voltages measured at the source side (rectified mains supply) and the load side. A safety margin to balance inaccuracies of the measurement is added to this calculated point of time.
In accordance with another object of the invention to minimize distortion and harmonics a fine adjustment of the energy transfer through fine tuning of the pulse width of the shunt switch is introduced overcoming the limitations of discrete time steps in clocked digital systems. This is achieved by either using patterns or by a digital delta sigma modulator that is averaging the ON time values of the shunt switch by toggling between neighboring ON time values (pulse-width) and controlled by said digital control unit.
In accordance to the object of this invention the calculation of the point of time of the zero current state of the storage inductor and the fine-tuning of the energy transferred require a very high accuracy of the measurement of the voltages at the load side, the inductor side and at the source side. This is achieved by a calibration of the tolerances of the voltage dividers used for these measurements. The voltage divider ratios can be measured at appropriate periods of time (see FIG. 7) considering the small influence of the voltage of the forward bias of the diode in the magnitude of 0.7 volt hence. This calibration enables the usage of tolerant voltage dividers. Said digital control unit is controlling the calibration of said voltage dividers.
In accordance with the objects of the invention said three methods of (1) calculating the point of time of the zero state of the storage inductor and (2) of fine tuning the energy transfer and (3) of calibrating the voltage dividers to improve the accuracy of the voltages measured can all be used separately or used in any combinations together.